Forum

[Geraintosaurus]

Hi all,

I've had a backfire problem with my 2000 Bullet 500 for a while that I'm getting increasingly anxious about. It only happens in the low revs range, mostly as/just after I downshift. In addition, recently I noticed the bike feeling like it's about to stall when going up a gentle incline at low revs. I also think I can hear a sort of light clanking sound coming from the engine - possibly the piston is hitting the cylinder head due to poor ignition timing? - but I haven't had the bike long enough to know if it's normal. It's not too loud, but audible over the engine noise.

I've changed the spark plug but I haven't adjusted the gap as it's the resistor version and my manual only has gap recommendations for the non-resistor version. I don't think it's a spark plug problem though, but what do I know?

Anyone know a way of diagnosing this? Assuming it's timing, any idea which way I need to rotate the timing plate (or whatever it's called), or how I might find out? Or might I need to fiddle with the carb? I have a mikcarb - will I need to get new jets and if so how do I know which ones?

Thanks in advance - it's hard to enjoy the ride when I'm thinking about the damage to my precious exhaust or any damage it's doing to the cylinder!

Geraint

[Geraintosaurus]

Oh - one other thing - I've been trying to understand setting ignition timing and have read about setting it in the 'fully advanced' position, and apparently this is where the bike 'spends most of its time'. It seems like to access this setting I have to take off the timing plate thing using a special tool on the cam? Basically I have no idea what this means, can anyone help or direct me to a good video/manual?

[Geraintosaurus]

Oh and I have a conical air filter which might affect carb tuning. But the bike came with this and didn't have issues then so I don't think it's the direct cause.

[Geraintosaurus]

Final PS: I'm not sure if backfiring is the right word - sputtering maybe? Don't know if those two things are the same, but it's usually not too loud and sounds more...well more sputtery. And I have a sports exhaust, so I'm told, just not sure which...

[papasmurf]

A bit of popping and crackling in the exhaust is par for the course on big singles of British, (Indian) Origin.

But "pinking" in the combustion chamber when under load is serious in the long term:-



Also called spark knock, preignition or detonation. If left uncorrected it can ruin the motor. Caused by either a lean fuel condition, carbon deposits in the combustion chamber, over advanced ignition timing, wrong spark plugs, or overheating.

[Adrian]

Question re the backfiring? Is that popping and banging in the exhaust, or is it actually spitting back through the carburettor?



A "light clanking sound" suggests mechanical rather than pre-ignition, it could be a slack primary chain, these make a bit of racket as the chain adjuster clatters against the alloy chaincase. If it's constant you could have a big end failing, though a loose alternator rotor can make some expensive sounding noises.



As long as it stays in one piece the piston will not hit the head, however badly your ignition timing is out, once it reaches the top of its stroke it goes back down again. Running with the ignition too far out will damage the piston, though.



Your incline problem might be caused by "lugging" the engine at low revs in too high a gear, use the gearbox and appropriate revs. The big single engine might have plenty of torque but don't abuse it in this way any more than you would by over-revving it.



I get the impression that your Bullet has come as something of a culture shock. You might want to gen up a bit by reading some classic literature on the subject of old motorcycles from the practical point of view. May I suggest a copy of the 1950's classic "Motorcycles and How to Manage Them"? As your Bullet is essentially a 1950's motorcycle it might be very helpful. There are several copies on ebay at the moment. If you haven't already got them, an owner's manual and a workshop manual would be a good idea too.



A.

[Geraintosaurus]

Thanks papasmurf - looking at my manual, it says too far advanced ignition timing may also cause kick back when starting. I get this occasionally - should I be getting it at all? And it kicks back quietly, as in it doesn't sound like it's 'ignited' per se but maybe I wouldn't hear it anyway?

[Geraintosaurus]

Hi Adrian - this book sounds like a brilliant idea - thanks!



I had a feeling it might be a rider problem with the engine lugging - I guess it just sounds 'healthier' to me in the low revs so I try to keep it there but that's probably a mistake.



I think the sound is coming from the cylinder, but I will just go turn it on to make sure.

[Geraintosaurus]

I've read Zen and the Art of Motorcycle Maintenance but that turned out to be more zen than motorcycle maintenance...

[Geraintosaurus]

Oh, sorry, I missed your question about the backfiring. I only get smoke through the carburettor when trying to kickstart, occasionally. Otherwise it's a sort of low rumble from the exhaust.



Having just put my head next to the cylinder, the noise is coming from there I think but now I'm wondering if perhaps it's just the ignition itself... hard to say but it sounds vaguely more like a pop now than a metallic clang. I just noticed it suddenly one day and so assumed it was a problem but I might be over-reacting.